1. Field of the Invention
The present invention relates to orthogonal frequency division multiple access (OFDMA) technology applied, for example, to wireless transmission systems. The present invention relates to scheduling the transmission power and/or the bandwidth to maximize the proportional fairness in a wireless transmission.
2. Description of the Related Art
Wireless transmission systems based on OFDMA, such as those defined by the IEEE 802.16 family of standards, are being developed for commercial applications. OFDMA schemes allow multiple users to concurrently transmit in the same time slot by sharing the bandwidth and transmission power. Various OFDMA channel allocation schemes have been proposed to exploit different channel properties such as frequency selective fading. For instance, Adaptive Modulation and Coding (AMC) schemes give each user a set of subchannels that are “close” and have similar characteristics to exploit diversity. Other “Distributed” schemes such as Partial Usage of SubChannels (PUSC) and Full Usage of SubChannels (FUSC) give users subchannels that are spread across the available band to average out the differences between different subchannels. The latter class of subchannelization schemes make the quality of different subchannels approximately the same and thus “flattens” the subchannels between the base station and a user.
In either case, it is necessary to choose an allocation of subchannels for users and to allocate transmission power levels to these users. For example, it may be desirable to balance individual quality of service (QoS) levels and “fairness” among the users, and to also maximize system capacity. Since two resources (bandwidth and power) might be optimized, a simple notion of fairness might not be useful, so the proportional fairness and capacity can be used. For example, the proportionally fair optimal point is chosen so that no user can increase their proportional rate (new rate/current rate) without hurting the other users.
A radio resource scheduler typically performs the allocation of subchannels and transmission power function for each time-slot, in real-time. In the OFDMA framework, typically the scheduler has to provide the bandwidth and transmission power allocation based on current channel conditions within strict time constraints.